1. Field of the Invention
The present invention relates to an arc welding robot control system continuously changing welding conditions of an arc welding robot.
2. Description of the Related Art
Hitherto, in arc welding using an arc welding robot, in order to change welding conditions such as a welding current, a welding voltage, a welding speed, a weaving cycle, a weaving amplitude, and the like in stages, it has been required to specify (teach) a plurality of welding-condition changing positions (teaching positions) and to set such welding conditions, which vary from one welding-condition changing position to another, by hand. Since it is so complicated to change welding conditions by hand at every position where welding conditions need to be changed, there have been developed some techniques for changing welding conditions automatically (refer to Japanese Unexamined Utility Model Registration Publication No. S61-138470 and U.S. Pat. No. 6,177,650).
The technique disclosed in Japanese Unexamined Utility Model Registration Publication No. S61-138470, for example, is such that welding conditions of an arc welding robot are changed linearly based on a travelling distance of the welding robot. And, the technique disclosed in U.S. Pat. No. 6,177,650 is such that start and finish points, where welding conditions are changed, are set, welding conditions for each of the start and finish points are set, and then the welding conditions set for the start point are gradually changed so as to meet the welding conditions set for the finish point when a welding torch arrives at the finish point.
In the prior arts disclosed in the above two patent documents, welding conditions are changed while a welding torch performs one cycle of weaving operation and command values of welding currents at both left and right ends of the weaving operation become different to each other, which causes a problem that the thickness of welding bead becomes deviated. In addition, even in the case that an arc welding robot is provided with an arc sensor, since actual values of welding currents at both left and right ends of the weaving operation are different to each other, its welding wire fails to follow a desired welding line and deviates therefrom. Furthermore, an actual weaving operation of a welding torch delays a bit with respect to the commanded weaving operation, and due to the delay the timing when the welding torch completes one weaving cycle and the timing when welding conditions such as a welding current and the like are actually changed deviate from each other, so welding currents at both left and right ends of the weaving operation do not agree with each other; the faster the weaving cycle becomes, the larger the thickness of welding bead becomes deviated.